In general, a flow path switching valve used in an energy recovery apparatus or the like is a means for opening and closing a flow path, to which various types of valve bodies are applied. As an example of them, there is a spool control valve of a linear spool valve device, disclosed in U.S. Pat. No. 5,797,429.
This spool control valve device is, as shown with 301 in FIG. 1, characterized in a structure that high pressure seawater or brine can be alternately supplied to high pressure vessels 305 as a spool type piston 303 plays.
Such a conventional control valve device 301 is configured to alternately discharge operating fluid in a sleeve type cylinder 307, i.e., seawater or brine to the high pressure vessel 305 by the spool type piston 303 reciprocating in the cylinder 307. Therefore, in the case where the operating fluid has low viscosity like seawater or brine, a certain gap exists between the inner circumference of the cylinder 307 and the outer circumference of the piston 303 in order to make the piston 303 smoothly slide in the cylinder 307, and thus there is a problem of unavoidable leakage of the operating fluid.
To solve this problem, there has been proposed a 3-directional poppet valve disclosed in U.S. Pat. No. 7,540,550, in which a poppet-shaped control valve is used to minimize the leakage between the cylinder and the piston, thereby having little leakage and improving energy efficiency. However, a plurality of actuators are needed corresponding to a plurality of poppet valves, and each actuator has to be separately controlled, thereby causing problems that the whole structure or control becomes complicated and the costs of equipment, maintenance, etc. increase.
As another example, there has been proposed not the foregoing reciprocation type control valve but a rotation type control valve disclosed in U.S. Pat. No. 7,600,535, in which an inner rotor is rotated by external power to open and close a flow path of a casing and the rotor, thereby acquiring a desired system response. However, the rotation type control valve must leave a certain gap between the rotor and the casing, and thus the leakage in the gap is inevitable. Accordingly, there is a problem that system efficiency is lowered due to the leakage.